Randomness Evaluation of the Improved 3D-Playfair (i3D) Cipher Algorithm

In cryptography, two things are highly valued to secure the exchange of communication. One is the secrecy of key generated by a cryptographic algorithm, and the other one is its ability to have an unpredictable sequence in the message. The i3D-Playfair is a symmetric block cipher algorithm designed to improve the existing 3D(4x4x4) Playfair cipher algorithm. The improvement focuses on securing the key and likewise enhancing the message encryption. Randomness determines the cryptographic strength of an algorithm. Evaluating the p-value in statistical tests identifies the binary sequence as random or non-random. This paper uses the five selected NIST Statistical Test Suites battery tests to get the probability p-value in determining the randomness of a binary sequence. NIST STS is a standard statistical test for randomness. The selected statistical tests are the following: frequency (monobit) test, frequency test within a block, runs test, the longest run test of 1’s in a block, and cumulative sums test. The experimental result shows that all the statistical tests have a passing p-value that is greater than 0.01 (p-value $\geq$0.01). Also, the p-value of p-values (POP) of all the statistical tests is greater than or equal to 0.0001, showing uniformity of p-values. The histogram of all the tests also shows that the p-value is normally distributed. Furthermore, results show that all the randomness tests conducted execute an acceptable proportion that is above 57 or was able to achieve a passing percentage above 95%. Thus, the proposed i3D-Playfair algorithm generates random numbers. It is then strongly suggested to implement i3D-Playfair Cipher in software applications and messaging to secure data transmission.